1. Field of the Invention
The invention relates to the field of noninvasive tomography and in particular is applied to tomographic methods and apparatus for simultaneous optical detection of blood flow velocity and vessel structure. Noninvasive in vivo imaging of blood flow dynamics and tissue structures with high spatial resolutions of the range of 2 to 10 microns is achieved in biological systems.
2. Description of the Prior Art
Accurate determination of location and flow velocity of moving particles in highly scattering media, such as biological tissues, is important for medical diagnostics. Development of a high resolution noninvasive technique for in vivo blood flow imaging with a resolution in the range of 2 to 10 microns is necessary for accurate microvascular monitoring. The ideal microvascular imaging technique must fulfill several requirements: (a) probe the underlying microcirculation at a user-specified depth in both superficial and deep layers; (b) distinguish arterial from venous flow; (c) detect blood flow changes rapidly; and (d) be safe, noninvasive, reliable and reproducible. Numerous approaches have been investigated including Doppler ultrasound, conventional angiography, laser Doppler flowmetry and magnetic resonance angiography. Each of these techniques however have their limitations. Conventional laser Doppler flowmetry, for example, has been used to measure mean blood perfusion in the peripheral microcirculation. However, because of strong optical scattering in biological tissue, laser Doppler flowmetry cannot identify blood flow velocity at discrete spatial locations with micron resolution. Although Doppler ultrasound imaging provides a means to resolve flow velocities at different locations in the scattering medium, the relatively long acoustic wavelength required for deep tissue penetration limits spatial resolution to approximately 200 microns.
Therefore, what is needed is a method and apparatus that may be used in vivo to determine flow velocities in a turbid or highly scattering medium such as biological tissues with spatial and velocity resolutions equal or greater than those obtained by other methods.